Changing sources and processes sustaining surface CO 2 and CH 4 fluxes along a tropical river to reservoir system

Soued, Cynthia; Prairie, Yves T.

Freshwaters are important emitters of carbon dioxide (inline-formulaCO2) and methane (inline-formulaCH4), two potent greenhouse gases (GHGs). While aquatic surface GHG fluxes have been extensively measured, there is much less information about their underlying sources. In lakes and reservoirs, surface GHG can originate from horizontal riverine flow, the hypolimnion, littoral sediments, and water column metabolism. These sources are generally studied separately, leading to a fragmented assessment of their relative role in sustaining inline-formulaCO2 and inline-formulaCH4 surface fluxes. In this study, we quantified sources and sinks of inline-formulaCO2 and inline-formulaCH4 in the epilimnion along a hydrological continuum in a permanently stratified tropical reservoir (Borneo). Results showed that horizontal inputs are an important source of both inline-formulaCO2 and inline-formulaCH4 (inline-formula>90 % of surface emissions) in the upstream reservoir branches. However, this contribution fades along the hydrological continuum, becoming negligible in the main basin of the reservoir, where inline-formulaCO2 and inline-formulaCH4 are uncoupled and driven by different processes. In the main basin, vertical inline-formulaCO2 inputs and sediment inline-formulaCH4 inputs contributed to on average 60 inline-formula% and 23 inline-formula% respectively to the surface fluxes of the corresponding gas. Water column metabolism exhibited wide amplitude and range for both gases, making it a highly variable component, but with a large potential to influence surface GHG budgets in either direction. Overall our results show that sources sustaining surface inline-formulaCO2 and inline-formulaCH4 fluxes vary spatially and between the two gases, with internal metabolism acting as a fluctuating but key modulator. However, this study also highlights challenges and knowledge gaps related to estimating ecosystem-scale inline-formulaCO2 and inline-formulaCH4 metabolism, which hinder aquatic GHG flux predictions.

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Soued, Cynthia / Prairie, Yves T.: Changing sources and processes sustaining surface CO2 and CH4 fluxes along a tropical river to reservoir system. 2021. Copernicus Publications.

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Rechteinhaber: Cynthia Soued

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